Grease composition



United States Patent O No Drawing. Filed Dec. 1, 1964, Ser. No. 415,1917 Claims. (Cl. 252-25) This invention relates to an improved lubricatingcomposition and more particularly to a lubricant having the consistencyof a grease suitable for high temperature lubrication.

The trend in design of modern aircraft has accentuated the need for alubricant having the consistency of a grease which will lubricateanti-friction bearings operating at high rotational speeds and hightemperatures. Considerable progress has been made in recent years inproducing improved thickened lubricants for aircraft. For example,lubricating compositions having the consistency of a grease are nowavailable for lubricating bearings operating at 10,000 to 20,000revolutions per minute at temperatures up to about 400 F. However, greatdifficulty has been encountered in producing a lubrieating compositionhaving the consistency of a grease which will effectively lubricatebearings operating at speeds of 10,000 to 20,000 revolutions per minuteand at temperatures up to about 600 F. for prolonged periods of time.

Since many of the lubricating characteristics of a thickened lubricantare imparted to the lubricant by the lubricating oil used in preparingthe lubricant, a lubricating oil is required which is thermally stableat temperatures in the order of 600 F. While some lubricatingcompositions having the consistency of a grease have been prepared bythickening mineral lubricating oils, especially hydrotreated minerallubricating oils, the volatility of mineral lubricating oils is suchthat as a general rule they do not give adequate lubrication attemperatures in the order of 600 F. over prolonged periods of time.Synthetic oils are substantially more resistant to thermal degradationthan mineral oils. Synthetic oils, particularly the polyorganosiloxanesknown as the silicone oils in addition to being more resistant tothermal degradation than mineral oils also have high viscosity indicesmaking their use at high and ambient temperatures especially desirable.Thus, the lubricating oil employed in the composition of this inventionis a synthetic lubricating oil.

Even though the synthetic lubricating oils have given improvedlubricants, some difliculty has been encountered in producing athickened synthetic lubricating oil which will give adequate lubricationof bearings operating at temperatures of 600 F. and speeds up to 20,000revolutions per minute over a prolonged period of time.

We have discovered that a lubricating composition having improvedlubricating characteristics for an extended period of time when used tolubricate bearings operating at temperatures up to about 600 F. andspeeds of 10,000 to 20,000 revolutions per minute can be obtained byincorporating into a synthetic lubricating oil in oil thickeningproportions the solid residual pyrolysis product of mercuricthiocyanate. Thus, the improved lubricating composition of our inventioncomprises a dispersion in a synthetic lubricating oil of a sutficientamount to thicken the lubricating oil to a grease consistency of thepyrolysis product of mercuric thiocyanate.

Mercuric thiocyanate is available commercially so that neither thecompound per se nor its method of preparation constitutes any portion ofthe invention. Mercuric thiocyanate is a white powder having a molecularweight "ice of 317. Upon the application of heat, mercuric thiocyanatedecomposes without melting. Mercuric thiocyanate upon decomposing swellsto many times its original volume. The decomposition product is anextremely fluify light yellow product. Pyrolysis of mercuric thiocyanatecan be conducted at any desired elevated temperature such as at atemperature of 800 to 1200 F. Heating is continued until completepyrolysis is effected as evidenced by no further noticeable change inthe product and no detectable emission of gas or vapor. While we do notwish to be limited to any theory with respect to what occurs whenmercuric thiocyanate is thermally decomposed, we believe that theresulting product is a mixture of compounds, at least one of which is achain polymer having an empirical formula (C H N and representedstructurally by the following formula where n is a number from 3 to 21.

According to C. E. Redemann and H. 1. Lucas, Journal of the AmericanChemical Society, volume 62, pages 843844 (194-0), the product formedupon the pyrolysis of vacuum dried mercuric thiocyanate correspondsclosely to a compact condensation product, triangular in form, withtwenty-one nuclei and a molecular formula of C126H21N175. Regardless ofthe theory with respect to what happens during the pyrolysis of mercuricthiocyanate, we have found that the pyrolysis product when incorporatedin a synthetic lubricating oil in an amount sufiicient to give acomposition having the consistency of a grease results in a compositionhaving a surprisingly long performance life.

The amount of the pyrolysis product of mercuric thiocyanate which we usemay vary depending upon the particular lubricating base employed andupon the characteristics desired in the ultimate composition. In anyevent, the amount of the pyrolysis product used is an amount sufiicientto thicken the lubricating oil to a grease consistency. In general thisamount comprises about 10 to about 40 percent by weight of the totalcomposition.

The synthetic lubricating oil which is employed in the composition ofthe invention is selected from the group consisting of the liquidpolyorganosiloxanes having a high phenyl content and diphenylmethylsilylend groups and polyaryl ethers. The polyorganosiloxanes can be obtainedby hydrolyzing and polymerizing a mixture of diphenylmethylchlorosilane,dimethyldichlorosilane and diphenyldichlorosilane preferably in a ratioof 1:1:1, respectively, according to procedures known to those familiarwith the art. While the polyorganosiloxanes are generally a mixture ofpolymers, a general formula repre senting the polymer mixture by anideal molecule is as follows:

ylsilyl end groups and a molecular weight of 954 is represented by theformula 3 s s) z iO[ 3 2 2 s s) 2 2 (C6155) z a Exemplary of thepolyaryl ethers which can be used are 4 the polyphenyl ethers, i.e.,m-bis(m-phenoxyphenoxy) benzene and m-bis (m-phenoxyphenoxy)phenylether.

The lubricating composition of this invention can contain conventionallubricant additives, if desired, to improve other specific properties ofthe lubricant without departing from the scope of the invention. Thus,the lubricating composition can contain an auxiliary thickening agent, afiller, a corrosion and rust inhibitor, an extreme pressure agent, ananti-oxidant, a metal deactivator, a dye and the like. Whether or notsuch additives are employed and the amounts thereof depend to a largeextent upon the severity of the conditions to which the composition issubjected and upon the stability of the synthetic lubricating oil basein the first instance. Since the polyorganosiloxanes, for example, arein general more stable than mineral oils, they require the addition ofvery little, if any, oxidation inhibitor. When such conventionaladditives are used they are generally added in amounts between about0.01 and abmout 5 percent by weight based on the weight of the totalcomposition.

In those instances when an auxiliary thickening agent such asfinely-divided amorphous silica, bentoniteorganic base compound oresterified siliceous solid is employed, it is added in amounts of about0.5 to about 5 percent by Weight.

In compounding a composition of the present invention, various mixingand blending procedures may be used. According to one embodiment of theinvention, the synthetic lubricating oil, the pyrolysis product ofmercuric thiocyana-te together with conventional lubricant additives, ifdesired, are mixed together at room temperature for a period of about tominutes to form a slurry. During this initial mixing period somethickening is evidenced. Some lumps may be formed. The slurry thusformed is then subjected to a conventional milling operation in a ballmill, a colloid mill, homogenizer or similar device used in compoundinggreases to give the desired degree of dispersion.

In order to illustrate the lubricating characteristics of a greasecomposition of the invention when used to lubricate bearings operatingat 600 F. and at rotational speeds of 20,000 revolutions per minute,Pope spindles were used in a test procedure similar to that outlined bythe Coordinating Research Council Tentative Draft (July 1954), ResearchTechnique for the Determination of Performance Characteristics ofLubricating Grease in Antifriction Bearings at Elevated Temperatures,CRC Designation L-35. According to the CRC L- test method, the testbearings are packed with 3.5 cc. (or equivalent weight) of grease.Because of the extremely short life of bearings packed with 3.5 cc. ofgrease, the present evaluations were made by packing the bearingscompletely full with about 6 to 8 grams of grease and using either astandard end cap with no additional grease or a special end cap holdinga reservoir of about 10 grams of additional grease. The hearing assemblycontaining an eight-ball SAE No. 204 ball hearing is mounted on ahorizontal spindle and is subjected to a radial load of 5 pounds. Theportion of the spindle upon which the test bearing assembly is locatedis encased in a thermostatically controlled oven. By this means thetemperature of the bearing can be maintained at a desired elevatedtemperature which in the tests reported hereinafter was 600 F. Thespindle is driven by a constant belt-tension motor drive assembly,capable of giving spindle speeds of 20,000 revolutions per minute. Thespindle is operated on a cycling schedule consisting of a series ofperiods, each period consisting of 20 hours running time and 4 hoursshutdown time. The test continues until the lubricant fails. Thelubricant is considered to have failed when any one of the followingconditions occurs, (1) spindle input power increases to a valueapproximately 300 percent above the steady state condition at the testtemperature; (2) an increase in temperature at the test bearing of 20 F.

4 over the test temperature during any portion of a cycle; or (3) thetest bearing locks or the drive belt slips at the start or during thetest cycle.

The lubricating oil used in preparing the lubricating compositions shownin Table I is a synthetic oil known as QF-67024 Fluid which is marketedby Dow Corning Corporation. This fluid is considered to be amethylphenylsiloxane polymer wherein the end silicon atoms aresubstituted to a high degree by two phenyl groups and one methyl group.The material is highly resistant to radiation. QF-6-7024 Fluid has astypical characteristics a viscosity at 100 F. of about 930 to 1030 SUS,a viscosity at 210 F. of about to SUS, a viscosity index of about 108 to110 and a pour point of +10 to +20 F. It is believed that the types ofside chains present and their approximate molar percentages (inparentheses) in QF-'67024 are phenyl (65), methyl attached throughsilicon to methyl (25) and methyl attached through silicon to phenyl(10). An ideal molecule of a polyorgano siloxane having this analysis isas follows:

The pyrolysis of mercuric thiocyanate used in preparing the illustrativecompositions of the invention was prepared according to the followingprocedure: A 4000 ml. Pyrex beaker cut to a height of 3 /2 inches wasplaced on a hot plate, the surface temperature of which was 1000il00 F.Into the beaker, 20 grams of mercuric thi-ocyanate were added slowly.Immediate partial pyrolysis of mercuric thiocyanate produced a blackcored yellow serpent-like elongation. Upon continued heating of thepartially pyrolyzed product with occasional stirring, a completelypyrolyzed fluffy light yellow product was obtained. The completelypyrolyzed mercuric thiocyanate thus obtained had a, melting point above450 C.

The Cab-O-Sil employed in preparing the compositions shown in Table I isa finely-divided amorphous silica marketed by Godfrey L. Cabot, Inc.This silica is a submicroscopic particulate silica prepared in a hotgaseous environment (1100 C.) by the vapor-phase hydrolysis of a siliconcompound. On a moisture-free basis, this silica is 99.0 to 99.7 percentsilicon dioxide which is practically free from contaminating metallicsalts. Gravimetric analyses fail to detect the presence of any calciumor magnesium. The iron content has been found to be about 0.004 percentand volatile matter removed on ignition at 1000 C. amounts to less than1 percent. Cab-O-Sil is an extremely fine silica with particles rangingin size from 0.15 to 0.020 micron.

In preparing the illustrative lubricating compositions, the oil, thepyrolysis product of mercuric thiocyanate and the silica were mixed atroom temperature for a period of 10 to 30 minutes. The slurry thusformed was passed twice through a Premier colloid mill set at astator-rotor clearance of 0.0015 inch. The approximate make-up andproperties of the thickened lubricating compositions thus prepared areset forth in Table I.

1 Results of two tests.

The long performance life of compositions of the inventron at a highrotational speed and a high temperature is self-evident from the abovedata.

Other lubricating compositions within the scope of the invention areillustrated in Table II. The polyaryl ethers show in Table II have thefollowing typical characteristics.

Viscosity, SUS:

At 100 F 1, 567 1, 691 8, 565 At 210 F-.-" 70 71 118 Four Poiut, F +35+40 +70 (1) m-Bis(m-phenoxyphenoxy)benzene. (2)Bis(phenoxyphenoxy)benzene (mixed isomers). (3)Bis-m(m-phenoxyphenoxy)pheny1 ether.

Table II Composition, percent by G D E F G H I .T

weight QF6-7024 87 75 Polyaryl Ether:

m-Bis(m-phenoxyphenoxy) Bbenfieneuuf1 3B.-- 85 81 is p enoxyp enoxyenzene (mixed isomers). 83 80 60 Bis-m(m-phenoxyphenoxy) phenyl ether 82Pyrolysis product of mercuric thiocyanate 10 12 14 16 18 19.5 25 40Cab-O-Si1 3 3 3 2 1 0.5

While our invention has been described with reference to variousspecific examples and embodiments, it will be understood that theinvention is not limited to such examples and embodiments and may bevariously practiced within the scope of the claims hereinafter made.

We claim:

1. A lubricating composition comprising a dispersion in -a major amountof a synthetic lubricating oil selected from the group consisting ofliquid polyorgano siloxanes having diphenylmethylsilyl end groups andpolyaryl ethers of a sufficient amount to thicken the lubricating oil toa grease consistency of the solid residual pyrolysis product of mercuricthiocyanate.

2. The lubricating composition of claim 1 wherein the pyrolysis productof mercuric thiocyanate comprises about 10 to about 40 percent by weightof the total composition.

3. A lubricating composition comprising a dispersion in a major amountof a liquid polyorganosiloxane having diphenylmethylsilyl end groups ofabout 10 to about percent by weight of the solid residual pyrolysisproduct of mercuric thiocyanate and about 0.5 to about 5 percent byWeight of finely-divided silica.

4. A lubricating composition comprising a dispersion in a major amountof a liquid polyphenyl ether of about 10 to about 40 percent by weightof the solid residual pyrolysis product of mercuric thiocyanate .andabout 0.5 to about 5 percent by weight of finely-divided silica.

5. A lubricating composition comprising a dispersion in a major amountof a synthetic lubricating oil selected from the group consisting ofliquid polyorganosiloxanes having diphenylmethylsilyl end groups andpolyaryl ethers of a sufiicient amount to thicken the lubricating oil toa grease consistency of the solid residual pyrolysis product of mercuricthiocyanate obtained by heating said mercuric thiocyanate at atemperature of about 800 to about 1200 F. for a time suflicient toefiect complete pyrolysis.

6. A lubricating composition comprising a dispersion in a major amountof la liquid polyorganosiloxane having diphenylmethylsilyl end groups ofabout 10 to about 40 percent by Weight of the solid residual pyrolysisproduct of mercuric thiocyanate obtained by heating said mercuricthiocyanate at a temperature of about 900 to about 1100 F. for .a timesuflicient to effect complete pyrolysis and about 0.5 to about 5 percentby weight of finely-divided silica.

7. A lubricating composition comprising a dispersion in a major amountof liquid polyphenyl ether of about 10 to about 40 percent by weight ofthe solid residual pyrolysis product of mercuric thiocyanate obtained byheating said mercuric thiocyanate at .a temperature of about 900 toabout 1100 F. for a time sufficient to efiect complete pyrolysis andabout 0.5 to about 5 percent by weight of finely-divided silica.

References Cited by the Examiner UNITED STATES PATENTS 3,089,875 5/1963Schroeder 447 3,108,957 10/1963 Murray et al. 25225 DANIEL E. WYMAN,Primary Examiner.

I. VAUGHN, Assistant Examiner.

3. A LUBRICATING COMPOSITION COMPRISING A DISPERSION IN A MAJOR AMOUNTOF A LIQUID POLYORGANOSILOXANE HAVING DIPHENYLMETHYLSILYL END GROUPS OFABOUT 10 TO ABOUT 40 PERCENT BY WEIGHT OF THE SOLID RESIDUAL PYROLYSISPRODUCT OF MERCURIC THIOCYANATE AND ABOUT 0.5 TO ABOUT 5 PERCENT BYWEIGHT OF FINELY-DIVIDED SILICA.